Just to save you some time: TrueCrypt 7.0a doesn’t work out of the box with Lion.

To get it running, follow these steps:

  1. Download & install TrueCrypt 7.0a for Mac
  2. Download & install: http://www.tuxera.com/mac/macfuse-core-10.5-2.1.9.dmg
  3. Reboot
  4. Use TrueCrypt